This invention pertains to methods of marking magnetic disks and the resulting disks.
Referring to FIG. 1, a typical magnetic disk 10 is manufactured by the following process.
1. Both sides of an aluminum alloy disk-shaped substrate 12 are coated, by electroless plating, with a NiP alloy layer 14.
2. The NiP alloy layer 14 is polished and textured.
3. An underlayer 16 (typically Cr, a Cr alloy, NiP, or other material) is sputtered onto NiP alloy layer 14.
4. A magnetic alloy layer 18 (typically a Co alloy) is sputtered onto underlayer 14.
5. A protective overcoat 20 (typically carbon or hydrogenated carbon) is sputtered onto magnetic alloy layer 18.
6. A lubricant layer is applied to protective overcoat 20.
Details concerning methods for manufacturing magnetic disks are described in U.S. patent application Ser. No. 08/984,753 now U.S. Pat. No. 6,150,015 filed by Bertero, et al. and incorporated herein by reference. (In lieu of NiP-coated aluminum alloy substrate 12, it is also known in the art to use a glass or glass ceramic substrate. In such processes, an underlayer, magnetic alloy and protective overcoat are typically deposited on the glass or glass ceramic substrate. A lubricant layer is then applied to the overcoat.)
As shown in FIG. 1, layers 14, 16, 18 and 20 are formed on both sides of substrate Occasionally, there is a defect on one side of disk 10 that renders that one side of the disk unusable while the other side of the disk is fully functional. There is a market for magnetic disks in which only one side is functional. However, after testing the disk, it is necessary to mark the defective side of the disk so that a disk drive manufacturer can tell which side should be used, and which side should not be used. In the past, a type of felt tip pen was used to mark the defective side of the magnetic disk.
Magnetic disks are made and tested in clean room environments, where elimination of dirt and other contaminants is of great importance. Accordingly, the felt tip pen is designed and used in a manner that minimizes such contamination. The pen is coupled to marking automation that receives a disk from a tester and marks the appropriate side of the disk. Unfortunately, the pen is prone to drying and running out of ink, and therefore, the disk must be inspected to ensure that the mark on the disk is visible.
It would be desirable to find an alternate means of marking the defective side of a disk. It is important that this method not create contaminants. In addition, this alternate means of marking the defective side of the disk must be reliable, fast and efficient.
A method for marking a defective side of a magnetic disk comprises the step of applying laser pulses to the defective side. The laser pulse parameters are selected so as to form marks having a rippled or crinkled appearance on the magnetic disk. However, the laser power and pulse duration are not so great as to result in the formation of a crater in the magnetic disk. I believe that during this process, the lubricant layer is evaporated from the portions of the disk surface which receive the laser pulse. I also believe that the ripple formation process may result from delamination of the sputtered films from the substrate, or the deformation of the NiP layer under the sputtered films, or both.
During a method in accordance with one embodiment of the invention, several rows of such laser marks are formed. These rows of laser marks are visible to the naked eye. Thus, disk drive manufacturers can easily see which side of the disk is defective.
In accordance with another embodiment, the laser marks are arranged in patterns other than rows. These patterns of laser marks ate also visible to the naked eye.
A process in accordance with my invention can be used to mark different types of magnetic disks, e.g. disks using metallic substrates, glass substrates, glass ceramic substrates, or other materials. The process can be used to mark disks having different types of layers, e.g. Co based magnetic layers, Fe based magnetic layers, carbon protective overcoats, ZrO2 protective overcoats, or different types of underlayers.
A marking process in accordance with some embodiments of the invention has one or more of the following advantages:
1. The laser marking process is reproducible.
2. The laser marking process is used to mark the defective side of magnetic disks without causing contamination.
3. Since a pen is not used, there is nothing that can dry out or run out of ink during use.
4. The laser marking process marks the defective side of the disk without affecting the functional side of the disk.
5. The laser marks are produced rapidly for enhanced manufacturing throughput.
6. The laser marks are readily visible to the naked eye. (This is important to the disk drive manufacturer, who must use the disk to assemble a working disk drive.)
7. The laser marking process can employ the types of lasers that are already in use in other areas of the disk manufacturing process. (Typically, lasers are used to texture magnetic disks prior to sputtering.)
8. The laser marking process can employ robotic manufacturing equipment to minimize the need, expense, and contamination problems that normally accompany human handling.
These and other advantages of the invention will be more readily apparent in light of the description below.